Dry reed switches are commonly comprised of two overlapping soft ferromagnetic electrically conducting cantilevers (reeds) separated by a small gap and supported by a glass hermetic enclosure. Upon application of a magnetic field the two opposing cantilevers are attracted to each other and establish electrical contact between the reeds. In the absence of a magnetic field the cantilevers resort to their original separated and electrically insulating state. Numerous electromechanical and electrical variations of this basic “single-pole, single-throw” normally open switch are used as well.
Various dry and wet reed switch designs have been proposed, for example those described in U.S. Pat. No. 7,321,282 “MEM's reed switch array”; U.S. Pat. No. 7,227,436 “Modular reed switch assembly and method for making”; U.S. Pat. No. 5,883,556 “Reed switch”; U.S. Pat. No. 5,847,632 “Reed switch”; U.S. Pat. No. 4,837,537 “Reed switch device”; U.S. Pat. No. 4,329,670 “Mercury reed switch”; and U.S. Pat. No. 4,039,985 “Magnetic reed switch”.
Conventional reed switch designs, however, can be costly to produce, and can exhibit a wide range of operating parameters even in switches of the same design. They are also generally constrained to specific relative orientations of the external electrical contacts and the applied magnetic field. For example, conventional glass encapsulated reed switches are fabricated with their leads extending axially from a cylindrically shaped glass ampule and are most sensitive to an externally applied magnetic field oriented along the axis of the leads.
Microfabricated reed switches have been proposed, for example in U.S. Pat. Nos. 5,430,421; 5,605,614, and 6,040,748. These generally rely on beam motion normal to the plane of deposition, which can pose difficulties in fabrication and packaging, for example by stress gradients in the materials that make consistent performance difficult to realize. Such designs also can suffer from problems with beam stiffness (i.e., it is generally desirable that the beam have a predictable stiffness in the direction of desired bending, and a high stiffness in other directions). Such designs also typically have a small anchor spot of the beam, resulting in low sensitivity to applied magnetic fields and consequently unacceptable performance (especially in miniature switches). Such designs also typically have coplanar external electrical connections, which can be unwieldy for use in surface mount electronics assembly.
The integrated reed switch described in this invention can be constructed to have more arbitrary orientation of its sensitive axis and electrical leads that can be oriented normal to and directly beneath the reed switch structure.